Simplified Seismic Design Methods for Low-Ductile Steel Multi-Tiered Concentrically Braced Frames
Isaac Derakhshan Houreh
Isaac completed his M.Sc. in structural engineering at the University of Alberta in 2020. With over six years of experience in the calculation and design of structures, he is currently a bridge/structural engineer at Stantec consulting services working on the analysis and design of infrastructures. His M.Sc. research at the University of Alberta aimed to evaluate the seismic behaviour of low-ductile Steel Multi-Tiered Concentrically Braced Frames (MT-CBFs) and to propose improved design recommendations for such frames in the framework of the Canadian Steel Design Standard, CSA S16.
Despite traditional CBFs, in MT-CBFs, more than one braced panels are stacked between the ground and roof levels. This configuration is commonly used in tall single-storey buildings when it is impractical or uneconomical to employ one braced panel for the entire frame height. A large portion of braced frame structures in Canada is located in low-to-moderate seismicity regions, where they are designed to provisions of low-ductile frames, namely Limited-Ductility (Type LD) braced frames and Conventional Construction (Type CC) category, to avoid relatively complicated seismic detailing. The special seismic design requirements for Type LD MT-CBFs in CSA-S16 require the column design forces to be determined using a series of nonlinear incremental analysis. Not only do these requirements seem too strict for such low-ductile frames, but the design procedure can become tedious or even complicated. Furthermore, no special requirements are required by CSA S16 for Type CC MT_CBFs. Based on the numerical analyses on a variety of frames, Isaac showed that the inelastic behaviour of these frames is limited. Thus he proposed enhanced and yet simplified seismic design methods for Type LD and Type CC MT-CBFs in regions of low-to-moderate seismicity of Canada.